Method for transferring heat in an aircraft engine thrust reverser

ABSTRACT

Thrust reverser inner wall structure comprising a thermally conductive nonmetallic carbon pitch fiber honeycomb core sandwiched between a top and bottom layer. The core is adhered by a reticulated layer of adhesive to a perforated carbon fiber top layer, and adhered to a base layer of nonmetallic, nonperforated carbon fiber reinforced fabric.

The present application is a divisional application based upon U.S.patent application Ser. No. 09/111,834, filed Jul. 28, 1995, now U.S.Pat. No. 6,210,773, which was a continuation application based upon U.S.patent application Ser. No. 07/926,444, filed Aug. 10, 1992, nowabandoned.

BACKGROUND OF THE INVENTION

A typical commercial airplane gas turbine engine includes a thrustreverser cowling nacelle. The nacelle structure consists of an inner andouter cowl joined with bifurcations. The engine fan airstream runsthrough the annular cavity between the two cowls. The inner cowl or wallcovers the engine case, accessories, and ducting installed therein.Because the engine case is very hot, up to 1100 degrees F., the insidesurface of the inner cowl, referred to as the thrust reverser innerwall, is exposed to high radiative energy.

Thrust reverser inner wall structures have generally been made withaluminum skin, an aluminum honeycomb core, and a layer of appliedinsulation on the hot surface adjacent to the engine case. This metallicthrust reverser inner wall has been effective in conducting heat awayfrom the engine to the surface adjacent to the fan airstream. A metallicstructure is heavy, resulting in a significant weight penalty. Inaddition, the aluminum is susceptible to corrosion damage.

To reduce the weight penalties and improve acoustic characteristics, thethrust reverser inner wall has been built with an aluminum honeycombcore sandwiched between carbon fiber layers. As a result of the carbonfibers adjacent to the aluminum core, the wall structure has beensusceptible to galvanic corrosion, particularly in the presence ofmoisture. Such corrosion creates a potential for subsequent structuralfailure of the aluminum core that is not acceptable.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a thrust reverser inner wallstructure that substantially reduces the weight penalty realized, avoidssusceptibility to corrosion, maintains the strength of the wall, andmaintains adequate thermal conductivity, thereby reducing the need forinsulation.

In accordance with the subject invention, a thrust reverser wall is asandwich structure with a top layer of epoxy impregnated perforatedcarbon fiber fabric, a non-metallic, composite honeycomb core, and abottom layer of epoxy impregnated carbon fiber fabric withoutperforations.

The non-metallic honeycomb core is made with pitch (based) carbon fibersto achieve the necessary thermal conductivity. The wall's high level ofthermal conductivity is such that the engine heat is conveyed to theperforated carbon fiber top layer. Engine fan air passing over the toplayer acts as a heat sink wherein enough heat is carried away from theengine to minimize the need for insulation on the engine side of thewall.

These advantages of the present invention will be more clearlyunderstood from the detailed description of the preferred embodimentthat follows taken in conjunction with the features shown in theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section of a typical commercial aircraft jet powerplant.

FIG. 2 is an isometric cut away view of the subject non-metallic thrustreverser inner wall.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As seen in FIG. 1, a typical commercial aircraft jet power plant 1comprises the engine 2, associated cowling 3, fan 4, and thrust reversercowling 5. The fan 4 draws air through the power plant 1 as indicated bythe fan air flow arrows 7. The fan air flow (7) enters cowling 3 andpasses through the annular fan air bypass duct 8 between the thrustreverser inner wall 10 and the thrust reverser outer wall 12.

While the power plant 1 is operating, the engine 2 generates asubstantial amount of heat and reaches up to 1100 degrees F. The insidesurface 14 of the thrust reverser inner wall 10 is directly exposed tothe high radiative energy. To reduce the need for insulation (not shown)on the inside surface 14, the subject thrust reverser inner wall 10 isdesigned to conduct the heat away from the engine 2, through the thrustreverser inner wall 10 to the relatively cold outer surface 16 Of thethrust reverser inner wall 10. The cold fan air flow 7 passing over theouter surface 16 acts as a heat sink. As such, high thermal conductivityof thrust reverser inner wall 10 results in less insulation and smallerweight penalties.

Weight penalties associated with the thrust reverser inner wall 10 arealso substantially reduced by utilizing composite materials for thehoneycomb core rather than aluminum or other metals. The thrust reverserinner wall 10 of the subject invention, as described below, maintainshigh thermal conductivity while utilizing all non-metallic components.

As seen in FIG. 2, thrust reverser inner wall 10 is a sandwich structurewith a top layer 20 of perforated carbon fiber reinforced epoxy.Perforations 22 are manufactured into the top layer 20 when the layer ispartially cured on a perforation layup tool (not shown). Theperforations 22 are designed to maintain proper acoustic properties ofthe thrust reverser inner wall 10. When installed in the power plant 1,the top face 24 of perforated carbon fiber top layer 20 directlyinterfaces with the fan air flow 7.

A layer of reticulated adhesive 26 adheres the perforated carbon fibertop layer 20 to a thermally conductive non-metallic carbon pitch fiberhoneycomb core 30. In the preferred embodiment, adhesive layer 26comprises BMS 5-137 Structural Adhesive for Acoustic Panels as definedin The Boeing Company specification BAC 5514-5137.

Thermally conductive non-metallic impregnated carbon pitch fiberhoneycomb core 30 consists of impregnated fabric reinforced sheets 32,corrugated to form specific honeycomb cells 35, then bonded with apolyimide adhesive resin and coated with a polyimide resin in accordancewith The Boeing Company specification BMS 8-339. The carbon pitch fiberhoneycomb core 30 has thermal conductivity ranging from 1.09-2.05 W/m−K,and, preferably, from 1.9 to 2.05 W/m×degrees K. This thermalconductivity characteristic transmits sufficient heat to be removed byfan airflow 7, thereby reducing the weight penalty associated with aresulting thick insulation layer.

The carbon pitch fiber honeycomb core 30 in the preferred embodiment, asspecified in The Boeing Company specification BMS 8-339, is manufacturedby Hexcel Corporation, Graham, Tex., as part numbers HFT-GP-327.Compared to an aluminum honeycomb core, the Hexcel carbon pitch fiberhoneycomb core 30 material reduces the weight penalty by 26% and is notsusceptible to corrosion.

A base layer 38 of non-metallic, nonperforated carbon fiber reinforcedfabric is adhered to the bottom surface 40 of carbon pitch fiberhoneycomb core 30 by a layer of adhesive 42. In the preferredembodiment, the adhesive used is BMS 8-245 Adhesive for CompositeBonding, as defined by The Boeing Company specification BMS 8-245.

The thrust reverser inner wall 10 sandwich structure described above isfabricated in accordance with The Boeing Company specification BAC5317-6.

The preferred embodiment of the thrust reverser inner wall 10 has aninsulation layer 45 adhered to the bottom of base layer 38, wherein theinsulation layer is the layer adjacent and closest to the engine 2 wheninstalled in the power plant.

While a particular embodiment of the invention has been described, itwill be apparent to persons skilled in the art to which this inventionpertains that many modifications and variations thereto are possiblewithout departing from the spirit and scope of the invention.

Accordingly, the scope of this invention should be considered limitedonly by the spirit and scope of the elements of the appended claims ortheir reasonable equivalents.

I claim:
 1. In an aircraft power plant, a method for conducting heatthrough a thrust reverser inner wall made from a honeycomb core sandwichpanel, comprising the steps of: (a) conducting heat from a carbon-fiberreinforced resin composite face sheet of the inner wall to a carbonfiber honeycomb core, the core having oriented carbon pitch fibers and athermal conductivity of about 1.09-2.05W/m−°K; and (b) conducting heatfrom the core to a perforated, fiber reinforced resin composite facesheet in contact with fan airflow for the aircraft power plant.
 2. Amethod for transferring heat from an aircraft engine to engine fan airin an engine nacelle, comprising the steps of: (a) orienting pitch basedcarbon fibers in a thrust reverser inner wall positioned between theengine and the fan air; (b) conducting heat from the engine to the fanair through the fibers to a perforated carbon fiber top layer; and (c)transferring heat from the top layer to the air passing over the toplayer.
 3. A method for reducing weight in a thrust reverser inner wallfor an aircraft engine, comprising the step of: reducing the volume ofinsulation for the inner wall by using pitch based carbon fibers in ahoneycomb core of the wall rather than aluminum honeycomb to conductheat from the engine to engine fan air to cool the wall and the engine.